1. Field of the Invention
This invention relates to a housing for a circuit breaker and more particularly to a novel and highly effective housing that is less expensive than conventional circuit breaker housings.
2. Description of the Prior Art
Circuit breakers have contacts capable of being in an open state or a closed state and of movement between the open and closed states. In the closed state they are intended to carry a current. When the current becomes excessive because for example of a short circuit, the circuit breaker is designed to open: i.e., the contacts move to the open state in order to interrupt the current and protect against a fire hazard and other damage that can result from a short circuit. In the case of a ground fault breaker, an imbalance of the current between phase and neutral indicates an alternative path to ground, and this imbalance trips the breaker. The alternative path to ground can be a person. Hence ground fault breakers are "personnel protectors."
When the contacts move in either direction between the open and closed states, arcing results (provided of course that power is supplied to the line side). That is because the contacts neither open nor close instantaneously but rather during a finite period (for example, a few milliseconds). As the contacts approach the closed state or move away from the closed state, there is a brief interval when an electrical current flows through the air gap between the contacts. This current flow through the air gap, called arcing, heats the air or gas in the vicinity of the contacts. The air or gas also contains molten contact material in a plasma state that is conductive.
Modern circuit breakers typically incorporate electronics modules for sensing ground fault conditions and generating a current to actuate solenoids to trip both poles of the circuit breaker in response to detection of a ground fault. Some of these components are susceptible to damage by the heated air that results from arcing. The housing for the circuit breaker should be constructed in such a way that these components are protected from the heated air and from the conductive properties of the plasma, which can bridge traces on the circuit board.
Not only that, but the housing for the circuit breaker must itself be able to withstand the heated air. For this reason, it is necessary to employ a heat-resistant material for the housing. In current practice, this material is normally a thermosetting plastic. Thermosetting materials can withstand the high temperature of the air or gas in the vicinity of circuit breaker contacts that are in the process of opening or closing.
The understanding of those skilled in the art is that thermoplastics, which can be injection molded from inexpensive materials in thin wall sections and using short cycle times, are unsuitable for use in making circuit breaker housings because thermoplastic materials are subject to melting or at least deformation by the gases resulting from arcing at the breaker contacts. Thermosetting materials, in contrast, maintain their shape even under arcing conditions.
However, thermosetting materials have certain disadvantages. One disadvantage is that the molding method employed to form the housing sections is a compression molding method requiring relatively thick wall sections and relatively lengthy cycle times during production. This increases the cost of circuit breaker housings made of thermosetting materials.
Another problem with conventional circuit breaker housings is that it is laborious and expensive to assemble the housing parts.